This application claims the benefit of Japanese Patent application No. 2001-062115 which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projection type display device constructed in a way that modulates and reflects color beams entering reflection type light valves disposed for a R (Red)-beam, a G (Green)-beam and a B (Blue)-beam and lets these beams exit, synthesizes and analyzes these color beams, and projects the color beam through a projection lens.
2. Related Background Art
An example of a construction of a prior art projection type display device will be explained. To begin with, a substantially parallel beam from a light source is polarization-split by a polarization beam splitter. Next, the thus polarization-split beam is color-separated into the R (Red)-beam, the G (Green)-beam and the B (Blue)-beam by a color separating optical system. The color-separated color beams such as the R-beam, G-beam and B-beam enter the light valves for the R-, G- and B-beams. The respective color light valves modulate the incidence beams in accordance with image signals and let the modulated beams exit. The reflected beams modulated by the light valves are color-synthesized by a color synthesizing optical system. Then, the color-synthesized beam reenter the polarization beam splitter and is analyzed. Finally, the analyzed beam exiting the polarization beam splitter is projected as a full-color image of the modulated image on a screen through a projection lens.
FIG. 11 is a view schematically showing a configuration of the projection type display device in the prior art and light paths therein. A light source 1 constructed of a lamp and a concave surface mirror such as a parabolic mirror, emits substantially parallel light source beam. The light source beam from the light source 1 enters a fly""s eye integrator FE. The fly""s eye integrator FE is constructed of a first lens plate 2 having a plurality of first lens elements 2a, 2b, 2c, and a second lens plate 3 having a plurality of second lens elements 3a, 3b, 3c corresponding to the first lens elements 2a, 2b, 2c. Herein, the second element elements 3a, 3b, 3c are provided in focal positions of the first lens elements 2a, 2b, 2c. With this construction, the beam from the light source 1 is, after being split, overlapped on the light receiving surfaces of light valves defined as the radiation receiving surfaces. A uniformity of illuminance of the illumination radiation can be thereby enhanced.
The beams exiting the fly""s eye integrator FE enter the polarization beam splitter 6 via a condenser lens 4 and a field lens 5. A polarized light splitting element 6P of the polarization beam splitter 6 reflects an S-polarized beam and transmits a P-polarized beam, thus polarization-splitting the beams. The S-polarized beam reflected by the polarized light splitting element 6P is discarded as an unnecessary beam.
The P-polarized beam exiting the polarization beam splitter 6 enters a color separating/synthesizing composite prism constructed of prisms 7, 8 and 9. The color separating/synthesizing composite prism color-separates the light source beam into the B-, R and G-beams. The structure for the color separation is the same as what is disclosed in, e.g., Patent Publication No. 2505758, and therefore its repetitive explanation is herein omitted.
The color-separated beams assuming the respective colors are incident on light valves 10B, 10R, 10G for the respective colors. The color light valves 10B, 10R, 10G modulate the incidence beams in accordance with image data and then let the modulated beams exit. The beams exiting the color light valves 10B, 10R, 10G enter the color separating/synthesizing composite prism and are color-synthesized. The thus color-synthesized beam enters the polarization beam splitter 6. The polarized-light splitting element 6P of the polarization beam splitter 6 reflects and analyzes the modulated beam (S-polarized beam) in the color-synthesized beam. The modulated beam reflected by the polarized-light splitting element 6P exits the polarization beam splitter 6. The modulated beam exiting the polarization beam splitter 6 enters a projection lens 11. The projection lens 11 projects images generated on the color light valves 10B, 10R, 10G as a full-color image on a screen 12.
In the projection type display device according to the prior art, light is absorbed by glass materials constituting the polarization beam splitter 6, and the prisms 7, 8, 9 of the color separating/synthesizing composite prism, a bonding agent for bonding the prisms to each other and an optical thin film for color-separating the incidence beams. With this light absorption, the polarization beam splitter 6, the prisms 7, 8, 9 get exothermic. With this heat emission, volumes of the optical elements expand. Herein, the optical elements such as the polarization beam splitter 6 and the prisms 7, 8, 9 are mechanically fixed to a frame or the like. Accordingly, stresses derived from the heat emission occur in interiors of the optical elements. Then, a polarized-light splitting characteristic declines due to these stresses. This results in such a problem that a contrast of the projected image decreases.
A relationship between the stresses derived from the heat emission and configurations of the light paths or the optical elements, will be explained in greater detail.
Referring to FIG. 11, the beams converged on the lens elements 3a, 3c of the second lens plate 3 that correspond to the outermost lens elements 2a, 2c of the first lens plate 2 receiving the incidence of the light source beams, form luminous points. Outermost marginal rays i1, i2 of the beams emerging from these luminous points travel through the condenser lens 4 and the field lens 5. Then, the two rays i1, i2 become the outermost marginal rays of the beam entering the polarization beam splitter 6.
Further, the light source beam traveling via the lens element 2b of the first lens plate 2 on an optical axis I is converged as a luminous point on the corresponding lens element 3b of the second lens plate 3. The beam from this luminous point on the second lens plate 3 becomes chief rays i0. The field lens 5 collimates the chief rays i0 into substantially parallel light rays. Then, the chief rays collimated into substantially the parallel light rays travel through the prisms 7, 8, 9 of the color separating/synthesizing composite prism and the color light valves 10B, 10R, 10G and are converged at an aperture stop (unillustrated) of the projection lens 11.
A size of each of incidence surfaces of the light valves 10B, 10R, 10G is 0.907 in., and a surface dimension of the incidence surface is given by 18.43 mm (width)xc3x9713.82 mm (length). In FIG. 11 showing the schematic geometry, a long side of the incidence surface of each of the light valves 10B, 10R, 10G is parallel with the sheet surface, while the short side is vertical to the sheet surface. This geometry will hereinafter be called a xe2x80x9clateral layoutxe2x80x9d.
FIG. 12A is a view showing a configuration in section perpendicular to the light source beam incidence surface 7a of the prism 7. The outermost marginal ray i1 enters, from the side of the surface 7a, the vicinity of an acute-angled xcex1 portion formed of the incidence surfaces 7a, 7b of the prism 7 taking substantially a shape of a triangular prism.
FIG. 12B is a view viewed from the side of the surface 7a of the prism 7. FIG. 12C is a view viewed from the side of the surface 7c of the prism 7. The B-beam in the beam entering the surface 7a is reflected by the surface 7b coated with the dichroic film reflecting the B-beam. Next, the B-beam is totally reflected by the surface 7a and thereafter exits the surface 7c. Therefore, as shown in FIG. 12B, an effective area 7d irradiated with the beam in the area of the surface 7a does not take a shape proportional to the configuration of the radiation element of the light valve and takes a shape enlarged in the longitudinal direction. Note that an apex portion, having an angle of 54 degrees, of the prism 7 does not, as shown in FIG. 12A, substantially transmit the beam. Hence, this portion assumes a shape cut, wherein a width of 3 mm from the effective portion of the illumination radiation is left.
FIG. 12D is a view showing a contrast decline portion N1 appeared on the projected image. The decline of contrast, when the projected image is displayed in black, becomes more conspicuous because of the contrast decline portion N1 becoming whitish.
The inventor of the present application analyzed internal stresses due to thermal expansions caused by the incidence of the beam with respect to the prism 7 in the projection type display device according to the prior art. An analysis model is calculated by use of a finite element method on the assumption that the beam with a uniform distribution totally enters the incidence surface 7a of the prism 7 in FIG. 12A. FIG. 13 qualitatively depicts directions and moments of the internal stresses occurred in the prism 7 by use of double-arrow lines. As obvious from FIG. 13, it proved that the stresses concentrate on the acute-angled xcex1 portion of the prism 7. Further, an absolute value of the stress is large in the vicinity M of the center of the acute-angled xcex1 portion in a direction of a height h. The stress in the vicinity M of the center occurs in the direction parallel to the height h of the prism 7.
Moreover, the inventor of the present application found out that the internal stresses occur in the upper and lower surfaces 7e, 7f of the prism so as to continuously link in the directions parallel with the upper and lower surfaces 7e, 7f. 
Note that the thermal stresses, as in the prism 7, occur in the optical elements such as the polarization beam splitter 6 and the prisms 8, 9. In the polarization beam splitter 6 etc, however, the number of passages of the beams through the same portion within each optical element is counted xe2x80x9c2xe2x80x9d in reciprocation, which is less than in the case of the prism 7. A light quantity of the beam traveling through the prisms 8, 9 decreases corresponding to a quantity of the beam reflected by the prism surface 7b. Therefore, both an exothermic quantity based on the light absorption and the thermal stress occurred are smaller than in the prism 7. Accordingly, it is apparent that the contrast of the projected image declines due to mainly the stresses occurred in the prism 7 exhibiting the maximum passage count of the beams.
The prism 7 has a function of synthesizing and analyzing the plurality of colors but has a large ununiformity in the projected image if the problem of the thermal stress rises, and exhibits a conspicuous decline of contrast.
It is a primary object of the present invention, which was devised in view of the problems described above, to provide a projection type display device capable of obtaining a projected image exhibiting no ununiformity and a preferable contrast with a simple construction.
To accomplish the above object, according to one aspect of the present invention, a projection type display device comprises an illumination optical system for supplying an illumination radiation, a polarization splitting/color separating optical system for polarization-splitting and color-separating beam from the illumination optical system, reflection type light valves, each taking a rectangular shape, for modulating the beam from the polarization splitting/color separating optical system in accordance with an image signal and letting the modulated beam exit, a color synthesizing optical system for color-synthesizing the beams from the reflection type light valves, a light analyzing optical system for analyzing the beam from the color synthesizing optical system, and a projection optical system for projecting on a predetermined surface an image based on the image signal generated in the reflection type light valves, wherein when the image signal indicates black, the color synthesizing optical system and the light valve are positioned so that a color of a predetermined point in the vicinity of an apex but inside of the apex of a rectangular display area on the predetermined surface, becomes a color of such a coordinate value that a distance of a color in the position corresponding to the center of the light valve is equal to or less than 0.09 from the coordinate value in a uxe2x80x2vxe2x80x2 space. Herein, the uxe2x80x2vxe2x80x2 space is defined as a coordinate space in a uxe2x80x2vxe2x80x2 chromaticity diagram. The uxe2x80x2vxe2x80x2 chromaticity diagram is the same as CIE1976UCS chromaticity diagram as well as being a coordinate system close to a human sensation to a color difference and created so that a color difference sensed by human eyes is substantially proportional to a difference between coordinate values on the chromaticity diagram. The projected image is recognized essentially by the human eyes, and hence this coordinate system is herein used as a basis for representing the colors. Further, a distance of a certain point (ux, vx) from central coordinates (uc, vc) is expressed by the following formula (1):
Distance={(uxxe2x88x92uc)2+(vxxe2x88x92vc)2}1/2xe2x80x83xe2x80x83(1)
In the projection type display device of the present invention, when the image signal indicates black, a color separating/synthesizing optical system and the light valves are positioned so that the color of the predetermined point in the vicinity of an apex but inside of the apex of a rectangular display area on the predetermined surface, becomes a color of such a coordinate value that a distance of a color in the position corresponding to the center of the light valve is equal to or less than 0.04 from the coordinate value in the uxe2x80x2vxe2x80x2 space.
In the projection type display device according to the present invention, it is preferable that the reflection type light valve includes a reflection type light valve for a blue beam and a reflection type light valve for a long wavelength region, upon which the beam in the longer wavelength region than the blue beam is incident, the color synthesizing system includes a first prism and a second prism, the first prism receives an incidence of the beam from the light valve for the long wavelength region and lets the beam exit, and the second prism receives an incidence of the beam from the light valve for the blue beam, then receives an incidence of the beam exiting the first prism, synthesizes the blue beam entering the second prism with the beam in the long wavelength region and lets the synthesized beam exit toward the light analyzing optical system.
In the projection type display device according to the present invention, it is preferable that the color synthesizing optical system includes a prism, the prism has a first surface totally reflecting the beam from the reflection type light valve, and a second surface receiving an incidence of the beam after the beam from the light valve has been reflected by a dichroic film, and the first surface is flush with the second surface.
In the projection type display device according to the present invention, it is preferable that the prism of the synthesizing optical system has an apex angle of 45 degrees or smaller.
In the projection type display device according to the present invention, when the image signal indicates black, the color synthesizing optical system and light valves are positioned so that a color of any one of points in the rectangular display area on the predetermined surface, becomes a color of such a coordinate value that a distance of a color in a position corresponding to the center of the light valve is equal to or less than 0.09 from a coordinate value in the uxe2x80x2vxe2x80x2 space.
In the projection type display device according to the present invention, when the image signal indicates black, the color synthesizing optical system and light valves are positioned so that a color of any one of points in a rectangular display area on the predetermined surface, becomes a color of such a coordinate value that a distance of a color in the position corresponding to the center of each light valve is equal to or less than 0.04 from the coordinate value in the uxe2x80x2vxe2x80x2 space.
In the projection type display device according to the present invention, the predetermined point is a point at which to divide, at a ratio of 9 to 1, a distance between the position corresponding to the center of each light valve in the rectangular display area on the predetermined surface and the apex of the rectangular display area.